Heartland Payment Systems (HPY) on Tuesday disclosed that intruders hacked into the computers it uses to process 100 million payment card transactions per month for 175,000 merchants.

Robert Baldwin, Heartland's president and CFO, said in a USA TODAY interview that the intruders had access to Heartland's system for "longer than weeks" in late 2008. The number of victims is unknown. "We just don't have the information right now," Baldwin said.

Tech security experts said the breach could set a record. Retail giant TJX lost 94 million customer records to hackers in 2007. With more than 100 million transactions per month, they could discover that several months' worth of transactions were captured, says Michael Maloof, chief technology officer at TriGeo Network Security.

Heartland processes card payments for restaurants, retailers and other merchants. It discovered the hack last week after Visa and MasterCard notified it of suspicious transactions stemming from accounts linked to its systems. Investigators then found the data-stealing program planted by the thieves.

"Our discussions with the Secret Service and Department of Justice give us a pretty good indication that this is part of a group that appears to have done security breaches at other financial institutions," said Baldwin. "This is a very sophisticated attack." Once it sorts out the matter, Heartland plans to notify each victim whose data were stolen to comply with data-loss disclosure laws in more than 30 states, Baldwin said.

"Cleaning up the mess could be potentially much more expensive than any fines or penalties," says Michael Argast, senior analyst at security firm Sophos.

Heartland's disclosure coincides with reports of heightened criminal activities involving stolen payment card numbers. Security firm CardCops has been tracking a 20% year-over-year increase in Internet chat room activity where hackers test batches of payment card numbers to make sure that they're active. "The numbers could have come from a processor, like Heartland, or some other source that has access to a lot of customer data but is not a retailer," says Dan Clements, CardCops president.

Also, Forcht Bank in Kentucky last week began issuing replacement debit cards to 8,500 patrons, due to reports of fraudulent card activity. "There are several other banks affected, and this is not isolated to Forcht Bank customers," the bank said in a Jan. 12 statement to customers.

To report corrections and clarifications, contact Reader Editor Brent Jones. For publication consideration in the newspaper, send comments to letters@usatoday.com. Include name, phone number, city and state for verification. To view our corrections, go to corrections.usatoday.com.

Guidelines: You share in the USA TODAY community, so please keep your comments smart and civil. Don't attack other readers personally, and keep your language decent. Use the "Report Abuse" button to make a difference. Read more.